bottomless pit vs limbo

bottomless pit

noun
  • A person with an apparently boundless appetite; an entity or problem which consumes seemingly endless resources. 

  • An endless resource or supply. 

  • Hell. 

  • A pit with no visible bottom (apparently-infinite depth). 

limbo

noun
  • Any in-between place, state or condition of neglect or oblivion which results in an unresolved status, delay or deadlock. 

  • A dance in which dancers take turns crossing under a horizontal bar or stick. The stick is lowered with each round, and the game is won by the player who passes under the bar in the lowest position. 

  • The place where innocent souls exist temporarily until they can enter heaven, notably those of the saints who died before the advent of Christ (limbus patruum) and those of unbaptized but innocent children (limbus infantum). 

verb
  • To dance in this way. 

How often have the words bottomless pit and limbo occurred in a corpus of books? (source: Google Ngram Viewer )